typedef struct A_stm_ *A_stm;
typedef struct A_exp_ *A_exp;
typedef struct A_expList_ *A_expList;
typedef enum {A_plus,A_minus,A_times,A_div} A_binop;

struct A_stm_
{
    enum {A_compoundStm, A_assignStm, A_printStm} kind;
	union 
	{
	    struct {A_stm stm1, stm2;} compound;
        struct {string id; A_exp exp;} assign;           
	    struct {A_expList exps;} print;        
	} u;
};
A_stm A_CompoundStm(A_stm stm1, A_stm stm2);
A_stm A_AssignStm(string id, A_exp exp);
A_stm A_PrintStm(A_expList exps);

struct A_exp_ 	
{
    enum {A_idExp, A_numExp, A_opExp, A_eseqExp} kind;
    union 
	{   
       string id;
       int num;
       struct 
	   {
	   		A_exp left; A_binop oper; A_exp right;} op;
            struct {A_stm stm; A_exp exp;} eseq;
       } u;
};
A_exp A_IdExp(string id);
A_exp A_NumExp(int num);
A_exp A_OpExp(A_exp left, A_binop oper, A_exp right);
A_exp A_EseqExp(A_stm stm, A_exp exp);

struct A_expList_ 
{
	enum {A_pairExpList, A_lastExpList} kind;   
	union 
	{
	   struct 
	   {
	       A_exp head;
		   A_expList tail; 
	   }pair;
       A_exp last;
    } u;
};

A_expList A_PairExpList(A_exp head, A_expList tail);
A_expList A_LastExpList(A_exp last);

